Many crystal oscillator circuits require biasing, amplitude control, and negative resistance circuits, which are made from individual components. For example, the biasing circuit may have components that are independent from the components used by the negative resistance circuit. By having separate circuits performing different functions, the area and power consumption of the crystal oscillator circuits are relatively large.
The use of individual circuits requires coupling capacitors between many of the individual circuits. Flux capacitors are required in many of these coupling applications. One problem with the coupling circuits is that the flux capacitors are very large and may consume a relatively large portion of the area of the die. For example, in a specific implementation in a 130 nm CMOS process, a crystal oscillator on a die may have an area of approximately 0.07 mm2. These crystal oscillators typically require at least three flux capacitors, which account for 0.03 mm2 or almost half of the die area.